Erosion Control Blankets and Seeding Wildflowers on Slopes
If your seeding project includes an area of steep slopes, then you will need to consider how to hold your investment in place. A slight slope (less than 25 or 30%) can be stabilized with a light mulching of straw (such as wheat stubble) or other mulch material (such as pine needles or bark chips). A 25% slope means that there is a 2.5-foot change in elevation for every 10 feet in distance up or down the slope (or 3 inches of elevation change for every foot of distance). The Natural Resource Conservation Service (NRCS), a part of the USDA, recommends the use of erosion control measures*, such as erosion control blankets, for any slope of 33% to 50%. Anything steeper than that will need rock riprap or terracing with retaining walls.
After seed germination, the roots of each new plant will interlock with one another below the surface, like laced fingers, to hold the soil in place. Above the ground, plant leaves and shoots will diffuse the direct impact of raindrops on the soil. But initially, steep slopes must be protected. Erosion control blankets, placed over recently seeded slopes, act to stabilize the soil to prevent seeds and soil from washing away and the cutting of erosion ruts into the hillside. Blankets prevent wind erosion and soil crusting and increase rainfall infiltration into the soil profile.
Erosion control measures also protect any streams, rivers, and lakes downhill from your site—and the wildlife that live there–from clouded water and silted bottoms. Plant seedlings can emerge through spaces within the blankets, when then disintegrate over time and leave a natural-looking vegetated slope behind.
What are they made of and where do you find them?
Erosion control blankets (ECB’s) come in various lengths and widths, with various netting materials, and various mulching materials. Most common is a thin plastic netting (one or two ply) that photodegrades over 1-3 years with an inner mulch layer of straw, excelsior (aspen shavings), or coir (coconut fiber). Straw or excelsior are best and both allow light to get through to seeds and soil. This is important because wildflower seeds are very small and each species has specific germination requirements, often involving day length and soil temperature.
The one-ply blankets containing straw tend to be the lowest price ($0.05-0.35 per square foot) depending on if the order includes shipping or not. Another good choice is excelsior batting. It is good since it also allows the light to the seeds and soil is one-ply containing excelsior (shredded aspen) and may be a little longer lasting than straw. The box store sources, like Lowe’s and Home Depot tend to be in the $0.15-0.17/sq ft range. When I was checking I found Home Depot had better prices than Lowes, but may depend on where you are…
Other online sources include Forestry Suppliers, Gempler’s, Erosion Control Products, and A.M. Leonard Horticultural Tool and Supply. These suppliers may offer blankets in the $0.05-0.10/sq ft range, but this price is before the shipping cost is added in.
A few notes about installing Erosion Control Blankets (ECB’s):
– Install the ECB only after soil preparation and seeding are complete.
– Remove all rocks or soil clods 1.5 inches or larger before installation.
– Leave at least a foot of extra blanket at the top of the slope for anchoring: dig a 6-inch deep trench across the top of the slope (or as deep as you can, if rocky soil), heaping the soil uphill from the trench; lay the extra blanket into the bottom of the trench, folding half of the extra underneath itself (like your curled fingers), pointing down the slope; cover the trench and top of the ECB with the soil; anchor with stakes. This keeps heavy runoff water from flowing under the blanket and washing out soil and seeds.
– The ECB should be anchored to the soil using metal wire staples or wooden stakes, driven through the blanket and remaining flush with the soil. Loose or sandy soil be a problem for anchoring the ECB – make sure the anchors are long enough to hold at the trench and seams.
– If you require multiple blankets running parallel down the slope, overlap the blanket edges with a minimum of a 4-inch overlap and stake or staple the seams periodically to ensure that no gaps develop from wind or rain.
–Check for any damage or displacement after a heavy rain.
For more information check out this USDA informational PDF (click image to view):